The argument that the claim morality is subjective is false because of its undesirable implications - so how can we know if slavery is right or wrong? - is an informal fallacy called the appeal to consequences. And that's a powerfully misleading motive for our wanting to insist that morality must be objective. It's an understandable misunderstanding.

So far, there's been no coherently argued objectivist response to my OP question.

I thought my response was clear. There is no way to justify any objective morality if we take the particular ontological assumptions upon which you insist for granted. Not only that, but there is also no legitimation for subjective morality, if we take those same ontological assumptions.

The argument that the claim morality is subjective is false because of its undesirable implications

This would not be my argument. While it is certainly true that subjectivism issues in some unsavoury, and indeed, impossible implications to live with in a practical way, this alone does not count against its truthfulness. I would have no argument with a subjectivist who lived as a pure Nihilist. I might still think he had a bad ontology, but at least he would be rationally consistent. Philosophically, that's all one could ask.

Rather, my argument would be that subjectivism can make no sense of the concept "morality" at all, and so is unequipped to offer anything by way of legitimating morality. Thus it is in no position even to pose the question, since it amounts to a denial of morality entirely.

For a subjectivist to ask about morality would be like an ordinary person asking about pixies.

...my argument would be that subjectivism can make no sense of the concept "morality"...

That's because your concept of "morality" is "What my god says". If morality is taken to mean, among other things, 'the intension not to argue in a way that is divisive and self-righteous', it is very easy to make sense of.

surreptitious57 wrote:
There initially needs to be some provisional axioms to establish the basis for morality ... The most obvious one is the principle of no harm ...

It is not obvious to Nietzscheans or Randians or Social Darwinists or elitists of all stripes or anybody who does not believe in the principle of the equality of persons. And there is a lot of these. Rather what is obvious to all of these groups is that people are NOT equal and in their view do
not deserve to be. The weak need to be down and the strong and wise need to be up. That seems very obvious to them

As I already said there needs to be some provisional axioms for the basis of morality to be established even if they are to be later discarded. The
aim therefore is not to determine absolute truth since that is not possible but one that has the broadest appeal and then work from that point on

The notion of egalitarianism is generally accepted as good and elitism is generally accepted as bad. So those types that you specifically mentioned
can be disregarded for that very reason in order to build the best possible morality which by implication has to be the best for as many as possible

I swear I've never come across such obtuseness, such a refusal to re-think an opinion in the face of rational argument. It's truly staggering. And I can see now that you're right. There is no hope. It's flogging an intellectually moribund horse.

The only benefit may be that everyone else following can make up their own minds.

As I already said there needs to be some provisional axioms for the basis of morality to be established even if they are to be later discarded.

Okay, but if we "later discard" them, then upon what is our moral legitimation founded? We've pulled back out our own foundations, and now have a morality floating on nothing.

What's really needed is a moral explanation that can be "drilled down" to the point at which we can safely say, "We know X is moral, because of this, that and the other. And when people ask how we know this, that or the other, we need to be able to say, "Because of these fundamental ontological facts about the universe."

Anything less will not rationally endure the first gesture of skepticism by anyone.

...the broadest appeal...

Would this be an argument to suggest that popularity = morality? I see no certainty in such a claim, if so. It seems to me likely to run afoul of the ad populum fallacy, does it not?

The notion of egalitarianism is generally accepted as good...

Not so. It's both very historically recent, and very local. Even today, it would not be a majority position on the world scene. For example, it is not generally accepted that women are equal to men, that children are equal to adults, or that members of a different tribe or social group are the moral equals of one's own. (We might snobbishly think this sort of view is confined to the "undeveloped world"; but note the alleged "basked of deplorables" said by some to exist in the US, for example: is that egalitarian?).

...and elitism is generally accepted as bad.

Only by those not benefitting from it. If you go to India and ask the Brahmins whether they are equal to Untouchables, I dare say they will say no. That situation is more typical on the world and historical scale than our "enlightened," 21st Century, Western values.

The view you're suggesting would probably place most people in world history on the outside. That doesn't make it wrong, but it certainly makes it in need of justification.

surreptitious57 wrote:
As I already said there needs to be some provisional axioms for the basis of morality to be established even if they are to be later discarded

Okay but if we later discard them then upon what is our moral legitimation founded

It is founded upon whatever the provisional axiom of the time is. This is not something set in stone rather an eternal self correcting process
that does not seek absolute truth but the best possible version of that truth. Which is exactly the same principle wrt how science progresses
This is ironic given that science has precisely nothing to say about morality. Though just like morality it also cannot determine absolute truth

...does not seek absolute truth but the best possible version of that truth....

The worry with that is that "best possible" is not an agreed-upon standard. Instead, what ordinarily happens is somebody smuggles in their OWN conception of what's "best" for us, and calls it "moral," then holds us to it -- the persuaders with rhetoric, and the enforcers with force, but neither having legitimated their claim to say what "best" is. Nietzsche saw that.

Which is exactly the same principle wrt how science progresses..

Well, perhaps not quite. After all, science has testing procedures. But how does one "test" to find out if, say, an independent UK is "best" or a UK merged with Europe is "best"? There will be "winners" and "losers" in either case; so whose interests really reflect the "best" for everybody else? Or how do we "test" to find out if slavery is wrong. If we ask the slave owners, they'll say their way of life depends on slavery, and it's best for their slaves as well, since slavery is the "best" use you can make of that kind of person. How do we beat that, since no neutral testing procedure exists for morality? Should we even beat it? How do we know we should?

Would this be an argument to suggest that popularity = morality ? I see no certainty
in such a claim if so. It seems to me likely to run afoul of the ad populum fallacy

There is no certainty in any moral truth regardless of how popular it is because morality and certainty are not compatible
But consensus is currently the fairest way to decide which moral truths are adopted [ within law ] and which are rejected

Immanuel Can wrote:
How do we beat that since no neutral testing procedure exists for morality

Morality is in a constant state of evolution and so is independent of any neutral or objective means of testing so it cannot be examined that way
It is an abstract concept with no rules but implicit within it is the notion of no harm as we discovered that this has practical benefits for society

But consensus is currently the fairest way to decide which moral truths are adopted [ within law ] and which are rejected

Here again, though, we have two problematic concepts: firstly, the idea of "fair," because we don't say who gets to say what "fair" is, and why. The second is that we have no pre-existing certainty that "consensus" is itself "good" in any durable sense. For there are surely times when the majority of people can be thought to be doing bad things, or thinking things that are untrue or perhaps immoral (assuming such actions exist).

The murder of the Kulaks in Russia might be a case like this. Blaming them for famine had the salutary effect of rallying the majority of people not to overthrow the government, and to have an object to blame for the Soviet mismanagement of the grain supply. No doubt the majority were be able to get behind such an explanation, and feel encouraged by it. But was it "fair"? Was it true? Was it good? Manifestly not, right?

Immanuel Can wrote:
How do we beat that since no neutral testing procedure exists for morality

Morality is in a constant state of evolution and so is independent of any neutral or objective means of testing so it cannot be examined that way

That makes the situation worse, not better. Now it's not just an unknown quantity, but a moving target, and unknowable quantity which won't ever stay the same. This way of describing the moral landscape would not give us anything to find at all, and no means even to go looking.

...implicit within it is the notion of no harm

We have seen that this notion is neither universal nor binding. There are powerful and intelligible ways of arguing that harm to some people can be justified. There is no universal agreement that harm is wrong.

...as we discovered that this has practical benefits for society

Two more problematic concepts appear here: "benefits"? For whom? And "society"? Whose?